Direct-LIT liquid crystal displays with laminated diffuser plates

ABSTRACT

In a directly-illuminated liquid crystal display (LCD), for example an LCD monitor or an LCD-TV, a number of light management films, including a diffuser layer, lie between the light source and the LCD panel to provide bright, uniform illumination. The diffuser layer is attached to a substrate which is separate from the light source and the LCD panel, or may be attached to either the LCD panel or, when using a two dimensional light source, to the light source. The other light management layers may also be attached to the separate substrate or to the LCD panel or two-dimensional light source. High levels of illumination uniformity at the LCD may be achieved with a uniform (non-patterned) diffuser, even with relatively low levels of diffusion, when the diffuser is used with a brightness enhancing layer.

RELATED PATENT APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/966,610, filed Oct. 15, 2004, now U.S. Pat. No. 7,446,827 nowallowed, the disclosure of which is incorporated by reference in itsentirety herein.

This application is related to U.S. patent application Ser. No.11/244,666, filed on Oct. 6, 2005, which is a continuation-in-part ofU.S. patent application Ser. No. 10/966,610, filed Oct. 15, 2004, nowallowed, the disclosure of which is incorporated by reference in itsentirety herein.

FIELD OF THE INVENTION

The invention relates to optical displays, and more particularly toliquid crystal displays (LCDs) that are directly illuminated by lightsources from behind, such as may be used in LCD monitors and LCDtelevisions.

BACKGROUND

Liquid crystal displays (LCDs) are optical displays used in devices suchas laptop computers, hand-held calculators, digital watches andtelevisions. Some LCDs include a light source that is located to theside of the display, with a light guide positioned to guide the lightfrom the light source to the back of the LCD panel. Other LCDs, forexample some LCD monitors and LCD televisions (LCD-TVs), are directlyilluminated using a number of light sources positioned behind the LCDpanel. This arrangement is increasingly common with larger displays,because the light power requirements, to achieve a certain level ofdisplay brightness, increase with the square of the display size,whereas the available real estate for locating light sources along theside of the display only increases linearly with display size. Inaddition, some LCD applications, such as LCD-TVs, require that thedisplay be bright enough to be viewed from a greater distance than otherapplications, and the viewing angle requirements for LCD-TVs aregenerally different from those for LCD monitors and hand-held devices.

Some LCD monitors and most LCD-TVs are commonly illuminated from behindby a number of cold cathode fluorescent lamps (CCFLs). These lightsources are linear and stretch across the full width of the display,with the result that the back of the display is illuminated by a seriesof bright stripes separated by darker regions. Such an illuminationprofile is not desirable, and so a diffuser plate is used to smooth theillumination profile at the back of the LCD device.

Currently, LCD-TV diffuser plates employ a polymeric matrix ofpolymethyl methacrylate (PMMA) with a variety of dispersed phases thatinclude glass, polystyrene beads, and CaCO₃ particles. These platesoften deform or warp after exposure to the elevated temperatures of thelamps. In addition, some diffusion plates are provided with a diffusioncharacteristic that varies spatially across its width, in an attempt tomake the illumination profile at the back of the LCD panel more uniform.Such non-uniform diffusers are sometimes referred to as printed patterndiffusers. They are expensive to manufacture, and increase manufacturingcosts, since the diffusing pattern must be registered to theillumination source at the time of assembly. In addition, the diffusionplates require customized extrusion compounding to distribute thediffusing particles uniformly throughout the polymer matrix, whichfurther increases costs.

SUMMARY OF THE INVENTION

One embodiment of the invention is directed to a directly illuminatedliquid crystal display (LCD) unit that includes a light source and anLCD panel. An arrangement of light management layers is disposed betweenthe one or more light sources and the LCD panel so that the light sourceilluminates the LCD panel through the arrangement of light managementfilms. The arrangement of light management layers comprises a diffuserplate, a brightness enhancing layer and a reflective polarizer. Thediffuser plate is positioned closer to the light source than thebrightness enhancing film and the reflective polarizer. The diffuserplate comprises a substantially transparent substrate attached to afirst diffusing layer that diffuses light propagating from the one ormore light sources towards the LCD panel.

Another embodiment of the invention is directed to a directlyilluminated liquid crystal display (LCD) unit that includes a lightsource and an LCD panel. An arrangement of light management layers isdisposed between the light sources and the LCD panel so that the lightsource illuminates the LCD panel through the arrangement of lightmanagement layers. The arrangement of light management layers comprisesat least one diffuser layer and a brightness enhancing layer. A singlepass transmission through the diffuser layer is greater than about 75%.

Another embodiment of the invention is directed to a directlyilluminated liquid crystal display (LCD) unit that includes an LCD paneland a flat fluorescent light source having an upper surface. The flatfluorescent light source is capable of emitting light through its uppersurface. An arrangement of light management layers is disposed betweenthe flat fluorescent light source and the LCD panel. The arrangement oflight management layers comprises at least a first diffuser layer and abrightness enhancing layer. At least one of the light management layersis attached to the upper surface of the flat fluorescent light source.

Another embodiment of the invention is directed to a directlyilluminated liquid crystal display (LCD) unit that includes a lightsource and an LCD panel comprising an upper plate, a lower plate and aliquid crystal layer disposed between the upper and lower plates. Thelower plate faces the one or more light sources and comprises anabsorbing polarizer. An arrangement of light management layers isdisposed between the light source and the LCD panel so that the lightsource illuminates the LCD panel through the arrangement of lightmanagement layers. The arrangement of light management layers comprisesat least a first diffuser layer, a brightness enhancing layer and areflective polarizer. At least one of the light management layers isattached to a lower surface of the lower plate of the LCD panel.

Another embodiment of the invention is directed to a directlyilluminated liquid crystal display (LCD) unit that includes a lightsource and an LCD panel. An arrangement of light management layers isdisposed between the light source and the LCD panel so that the lightsource illuminates the LCD panel through the arrangement of lightmanagement layers. The arrangement of light management layers comprisesa diffuser plate and at least one of a brightness enhancing layer and areflective polarizer. The diffuser plate comprises a substantiallytransparent substrate attached to a first diffusing layer that diffuseslight propagating from the light source towards the LCD panel.

The above summary of the present invention is not intended to describeeach illustrated embodiment or every implementation of the presentinvention. The figures and the detailed description which follow moreparticularly exemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 schematically illustrates a back-lit liquid crystal displaydevice that is capable of using a diffuser plate according to principlesof the present invention;

FIGS. 2A and 2B schematically illustrate embodiments of single sideddiffuser plates according to principles of the present invention;

FIGS. 3A and 3B schematically illustrate embodiments of double-sideddiffuser plates according to principles of the present invention;

FIGS. 3C and 3D schematically illustrate embodiments of diffuser plateswith double substrates, according to principles of the presentinvention;

FIGS. 4A-4G schematically illustrate additional embodiments of diffuserplates incorporating additional light management layers, according toprinciples of the present invention;

FIG. 5 schematically illustrates an embodiment of a diffuser assemblyattached to the lower plate of a liquid crystal panel, according toprinciples of the present invention;

FIGS. 6A-6C schematically illustrate embodiments of diffuser assembliesattached to a flat fluorescent light source, according to principles ofthe present invention;

FIG. 7 schematically illustrates an experimental set up used foroptically testing sample diffuser plates;

FIG. 8A presents a graph showing brightness uniformity plotted againstoverall brightness for control samples and example diffuser platesfabricated in accordance with principles of the present invention;

FIG. 8B presents a graph showing luminance as a function of positionacross a screen for a control sample and sample diffuser plates S1-S4;

FIG. 9 presents a graph showing luminance as a function of positionacross a screen for a control sample and sample diffuser plates S5, S8and S10;

FIG. 10 presents a graph showing luminance as a function of positionacross a screen for sample diffuser plates S2, S19, S21 and 26;

FIG. 11 presents a graph showing luminance as a function of positionacross a screen for sample diffuser plates S8, S20, S22 and 27;

FIG. 12 presents a graph showing brightness uniformity plotted againstoverall brightness for control samples and example diffuser platesfabricated in accordance with principles of the present invention, whenused with a brightness enhancing layer and a reflective polarizer;

FIG. 13 presents a graph showing luminance as a function of positionacross a screen for two control samples and sample diffuser plates S2and S8 when used with a brightness enhancing layer and a reflectivepolarizer;

FIGS. 14A and 14 B respectively present conoscopic plots for sample S28and control sample C3;

FIGS. 15A and 15B schematically present one embodiment of an arrangementfor fabricating a diffuser plate according to the present invention;

FIGS. 16A and 16B schematically present another embodiment of anarrangement for fabricating a diffuser plate according to the presentinvention;

FIG. 17 schematically presents another embodiment of an arrangement forfabricating a diffuser plate according to the present invention;

FIGS. 18A and 18B schematically present other embodiments ofarrangements for fabricating laminated assemblies used in diffuserplates of the present invention;

FIG. 19 presents a graph showing brightness uniformity plotted as afunction of single pass transmission through the diffuser plate forseveral sample uniform diffuser plates and for a printed diffuser plate;and

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

The present invention is applicable to liquid crystal displays (LCDs, orLC displays), and is particularly applicable to LCDs that are directlyilluminated from behind, for example as are used in LCD monitors and LCDtelevisions (LCD-TVs).

The diffuser plates currently used in LCD-TVs are based on a polymericmatrix, for example polymethyl methacrylate (PMMA), polycarbonate (PC),or cyclo-olefins, formed as a rigid sheet. The sheet contains diffusingparticles, for example, organic particles, inorganic particles or voids(bubbles). These plates often deform or warp after exposure to theelevated temperatures of the light sources used to illuminate thedisplay. These plates also are more expensive to manufacture and toassemble in the final display device.

The invention is directed to a directly illuminated LCD device that hasan arrangement of light management layers positioned between the LCDpanel itself and the light source. The arrangement of light managementlayers includes a diffuser plate having a rigid organic or inorganicsubstrate and a polymeric volume diffusing sheet possessing a specifictransmission and haze level directly adjacent to one side of thesubstrate. Another polymeric volume diffusing sheet may be positioned onthe other side of the substrate. The transmission and haze levels ofeach component are designed to provide a direct-lit LC display whosebrightness is relatively uniform across the display.

Diffuser plates of the present invention are simple to manufacture andprovide a high degree of flexibility in the materials and processes usedin manufacturing. In the diffuser plate according to the presentinvention, the structural and optical requirements are separated: thesubstrate provides the structural performance and the attached diffusinglayer, or layers, provides the optical performance. By separating thesefunctions, the cost advantages of using common transparent materials andcommon diffuser sheets can be exploited, to reduce overall costs. Thisalso permits the introduction of warp resistant plates, for exampleglass plates, at low cost. In addition, it is easier to control thediffusion properties more precisely when the diffuser is contained in alayer separate from the plate. Patterned diffuser films may also beapplied with less expense than with patterned, rigid, bulk diffuserplates.

A schematic exploded view of an exemplary embodiment of a direct-lit LCdisplay device 100 is presented in FIG. 1. Such a display device 100 maybe used, for example, in an LCD monitor or LCD-TV. The display device100 is based on the use of an LC panel 102, which typically comprises alayer of LC 104 disposed between panel plates 106. The plates 106 areoften formed of glass, and may include electrode structures andalignment layers on their inner surfaces for controlling the orientationof the liquid crystals in the LC layer 104. The electrode structures arecommonly arranged so as to define LC panel pixels, areas of the LC layerwhere the orientation of the liquid crystals can be controlledindependently of adjacent areas. A color filter may also be includedwith one or more of the plates 106 for imposing color on the imagedisplayed.

An upper absorbing polarizer 108 is positioned above the LC layer 104and a lower absorbing polarizer 110 is positioned below the LC layer104. In the illustrated embodiment, the upper and lower absorbingpolarizers are located outside the LC panel 102. The absorbingpolarizers 108, 110 and the LC panel 102 in combination control thetransmission of light from the backlight 112 through the display 100 tothe viewer. In some LC displays, the absorbing polarizers 108, 110 maybe arranged with their transmission axes perpendicular. When a pixel ofthe LC layer 104 is not activated, it may not change the polarization oflight passing therethrough. Accordingly, light that passes through thelower absorbing polarizer 110 is absorbed by the upper absorbingpolarizer 108, when the absorbing polarizers 108, 110 are alignedperpendicularly. When the pixel is activated, on the other, hand, thepolarization of the light passing therethrough is rotated, so that atleast some of the light that is transmitted through the lower absorbingpolarizer 110 is also transmitted through the upper absorbing polarizer108. Selective activation of the different pixels of the LC layer 104,for example by a controller 114, results in the light passing out of thedisplay at certain desired locations, thus forming an image seen by theviewer. The controller may include, for example, a computer or atelevision controller that receives and displays television images. Oneor more optional layers 109 may be provided over the upper absorbingpolarizer 108, for example to provide mechanical and/or environmentalprotection to the display surface. In one exemplary embodiment, thelayer 109 may include a hardcoat over the absorbing polarizer 108.

It will be appreciated that some type of LC displays may operate in amanner different from that described above. For example, the absorbingpolarizers may be aligned parallel and the LC panel may rotate thepolarization of the light when in an unactivated state. Regardless, thebasic structure of such displays remains similar to that describedabove.

The backlight 112 includes a number of light sources 116 that generatethe light that illuminates the LC panel 102. The light sources 116 usedin a LCD-TV or LCD monitor are often linear, cold cathode, fluorescenttubes that extend across the display device 100. Other types of lightsources may be used, however, such as filament or arc lamps, lightemitting diodes (LEDs), flat fluorescent panels or external fluorescentlamps. This list of light sources is not intended to be limiting orexhaustive, but only exemplary.

The backlight 112 may also include a reflector 118 for reflecting lightpropagating downwards from the light sources 116, in a direction awayfrom the LC panel 102. The reflector 118 may also be useful forrecycling light within the display device 100, as is explained below.The reflector 118 may be a specular reflector or may be a diffusereflector. One example of a specular reflector that may be used as thereflector 118 is Vikuiti™ Enhanced Specular Reflection (ESR) filmavailable from 3M Company, St. Paul, Minn. Examples of suitable diffusereflectors include polymers, such as polyethylene terephthalate (PET),polycarbonate (PC), polypropylene, polystyrene and the like, loaded withdiffusely reflective particles, such as titanium dioxide, bariumsulphate, calcium carbonate and the like. Other examples of diffusereflectors, including microporous materials and fibril-containingmaterials, are discussed in co-owned U.S. Patent Application Publication2003/0118805 A1, incorporated herein by reference.

An arrangement 120 of light management layers is positioned between thebacklight 112 and the LC panel 102. The light management layers affectthe light propagating from backlight 112 so as to improve the operationof the display device 100. For example, the arrangement 120 of lightmanagement layers may include a diffuser plate 122. The diffuser plate122 is used to diffuse the light received from the light sources, whichresults in an increase in the uniformity of the illumination lightincident on the LC panel 102. Consequently, this results in an imageperceived by the viewer that is more uniformly bright.

The arrangement 120 of light management layers may also include areflective polarizer 124. The light sources 116 typically produceunpolarized light but the lower absorbing polarizer 110 only transmits asingle polarization state, and so about half of the light generated bythe light sources 116 is not transmitted through to the LC layer 104.The reflecting polarizer 124, however, may be used to reflect the lightthat would otherwise be absorbed in the lower absorbing polarizer, andso this light may be recycled by reflection between the reflectingpolarizer 124 and the reflector 118. At least some of the lightreflected by the reflecting polarizer 124 may be depolarized, andsubsequently returned to the reflecting polarizer 124 in a polarizationstate that is transmitted through the reflecting polarizer 124 and thelower absorbing polarizer 110 to the LC layer 104. In this manner, thereflecting polarizer 124 may be used to increase the fraction of lightemitted by the light sources 116 that reaches the LC layer 104, and sothe image produced by the display device 100 is brighter.

Any suitable type of reflective polarizer may be used, for example,multilayer optical film (MOF) reflective polarizers; diffuselyreflective polarizing film (DRPF), such as continuous/disperse phasepolarizers, wire grid reflective polarizers or cholesteric reflectivepolarizers.

Both the MOF and continuous/disperse phase reflective polarizers rely onthe difference in refractive index between at least two materials,usually polymeric materials, to selectively reflect light of onepolarization state while transmitting light in an orthogonalpolarization state. Some examples of MOF reflective polarizers aredescribed in co-owned U.S. Pat. No. 5,882,774, incorporated herein byreference. Commercially available examples of MOF reflective polarizersinclude Vikuiti™ DBEF-D200 and DBEF-D440 multilayer reflectivepolarizers that include diffusive surfaces, available from 3M Company,St. Paul, Minn.

Examples of DRPF useful in connection with the present invention includecontinuous/disperse phase reflective polarizers as described in co-ownedU.S. Pat. No. 5,825,543, incorporated herein by reference, and diffuselyreflecting multilayer polarizers as described in e.g. co-owned U.S. Pat.No. 5,867,316, also incorporated herein by reference. Other suitabletypes of DRPF are described in U.S. Pat. No. 5,751,388.

Some examples of wire grid polarizers useful in connection with thepresent invention include those described in U.S. Pat. No. 6,122,103.Wire grid polarizers are commercially available from, inter alia, MoxtekInc., Orem, Utah.

Some examples of cholesteric polarizer useful in connection with thepresent invention include those described in, for example, U.S. Pat. No.5,793,456, and U.S. Patent Publication No. 2002/0159019. Cholestericpolarizers are often provided along with a quarter wave retarding layeron the output side, so that the light transmitted through thecholesteric polarizer is converted to linear polarization.

The arrangement 120 of light management layers may also include abrightness enhancing layer 128. A brightness enhancing layer is one thatincludes a surface structure that redirects off-axis light in adirection closer to the axis of the display. This increases the amountof light propagating on-axis through the LC layer 104, thus increasingthe brightness of the image seen by the viewer. One example is aprismatic brightness enhancing layer, which has a number of prismaticridges that redirect the illumination light, through refraction andreflection. Examples of prismatic brightness enhancing layers that maybe used in the display device include the Vikuiti™ BEFII and BEFIIIfamily of prismatic films available from 3M Company, St. Paul, Minn.,including BEFII 90/24, BEFII 90/50, BEFIIIM 90/50, and BEFIIIT.

Unlike conventional diffuser plates used in LCD-TVs, a diffuser plateaccording to an embodiment of the present invention has separatestructural and diffusing members. One exemplary embodiment of a diffuserplate 200 is schematically illustrated in FIG. 2A. The diffuser plate200 includes a substrate 202 and a diffuser layer 204 attached to thesubstrate.

The substrate 202 is a sheet of material that is self-supporting, and isused to provide support to the layers to which it is attached. Whileeach of the layers in a laminate contributes to the stiffness of thelaminate, the substrate is the layer that contributes most to thestiffness, i.e. provides more resistance to bending than any of theother layers of the laminate. A substrate does not significantly deformunder its own weight, although it may sag to a certain extent. Thesubstrate 202 may be, for example, up to a few mm thick, depending onthe size of the display. In one exemplary embodiment, a 30″ LCD-TV has a2 mm thick bulk diffuser plate. In another exemplary embodiment, a 40″LCD-TV has a 3 mm thick bulk diffuser plate.

The substrate 202 may be made of any material that is substantiallytransparent to visible light, for example, organic or inorganicmaterials, including glasses and polymers. Suitable glasses includefloat glasses, i.e. glasses made using a float process, or LCD qualityglasses, referred as LCD glass, whose characteristic properties, such asthickness and purity, are better controlled than float glass. Oneapproach to forming LCD glass is to form the glass between rollers.

The diffuser plate and one or more other light management layers may beincluded in a light management unit disposed between the backlight andthe LCD panel. The light management unit provides a stable structure forholding the diffuser plate and the one or other light management layers.The structure is less prone to warping than conventional diffuserplates, particularly if the supporting substrate is formed of awarp-resistant material such as glass. Also, the ability to supply adisplay manufacturer with a diffuser plate attached together with one ormore other light management layers as a single integrated unit resultsin simplified assembly of the display.

Suitable polymer materials may be amorphous or semi-crystalline, and mayinclude homopolymer, copolymer or blends thereof. Polymer foams may alsobe used. Example polymer materials include, but are not limited to,amorphous polymers such as poly(carbonate) (PC); poly(styrene) (PS);acrylates, for example acrylic sheets as supplied under the ACRYLITE®brand by Cyro Industries, Rockaway, N.J.; acrylic copolymers such asisooctyl acrylate/acrylic acid; poly(methylmethacrylate) (PMMA); PMMAcopolymers; cycloolefins; cylcoolefin copolymers; acrylonitrilebutadiene styrene (ABS); styrene acrylonitrile copolymers (SAN);epoxies; poly(vinylcyclohexane); PMMA/poly(vinylfluoride) blends;atactic poly(propylene); poly(phenylene oxide) alloys; styrenic blockcopolymers; polyimide; polysulfone; poly(vinyl chloride); poly(dimethylsiloxane) (PDMS); polyurethanes; poly(carbonate)/aliphatic PET blends;and semicrystalline polymers such as poly(ethylene); poly(propylene);poly(ethylene terephthalate) (PET); poly(ethylene naphthalate)(PEN);polyamide; ionomers; vinyl acetate/polyethylene copolymers; celluloseacetate; cellulose acetate butyrate; fluoropolymers;poly(styrene)-poly(ethylene) copolymers; and PET and PEN copolymers.

One or both sides of the substrate 202 may be provided with a mattefinish.

Exemplary embodiments of the diffusing layer 204 include a polymermatrix containing diffusing particles. The polymer matrix may be anysuitable type of polymer that is substantially transparent to visiblelight, for example any of the polymer materials listed above.

The diffusing particles may be any type of particle useful for diffusinglight, for example transparent particles whose refractive index isdifferent from the surrounding polymer matrix, diffusely reflectiveparticles, or voids or bubbles in the matrix. Examples of suitabletransparent particles include solid or hollow inorganic particles, forexample glass beads or glass shells, solid or hollow polymericparticles, for example solid polymeric spheres or polymeric hollowshells. Examples of suitable diffusely reflecting particles includeparticles of titanium dioxide (TiO₂), calcium carbonate (CaCO₃), bariumsulphate (BaSO₄), magnesium sulphate (MgSO₄) and the like. In addition,voids in the polymer matrix may be used for diffusing the light. Suchvoids may be filled with a gas, for example air or carbon dioxide.Commercially available materials suitable for use in a diffusing layerinclude 3M™ Scotchcal™ Diffuser Film, type 3635-70 and 3635-30, and 3M™Scotchcal™ ElectroCut™ Graphic Film, type 7725-314, available from 3MCompany, St. Paul, Minn. Other commercially available diffusers includeacrylic foam tapes, such as 3M™ VHB™ Acrylic Foam Tape No. 4920.

The diffuser layer 204 may be applied directly to the surface of thesubstrate 202, for example where the polymer matrix of the diffuserlayer 204 is an adhesive. In other exemplary embodiments, the diffuserlayer 204 may be attached to the surface of the substrate 202 using anadhesive layer 206, as is schematically illustrated in FIG. 2B. In someexemplary embodiments, the diffuser layer 204 has a diffusioncharacteristic that is uniform across its width, in other words theamount of diffusion experienced by light is the same for points acrossthe width of the diffuser layer.

The diffuser layer 204 may optionally be supplemented with an additionalpatterned diffuser 204 a. The patterned diffuser 204 a may include, forexample, a patterned diffusing surface or a printed layer of diffuser,such as particles of titanium dioxide (TiO₂). The patterned diffuser 204a may lie on the substrate 202, between the diffuser layer 204 and thesubstrate 202, or above the diffuser layer 204. The patterned layer 204a may be, for example, printed onto the diffuser layer 204, asillustrated in FIG. 2A, or onto a sheet that lies above the diffuserlayer 204.

The diffuser plate may be provided with protection from ultraviolet (UV)light, for example by including UV absorbing material or material in oneof the layers that is resistant to the effects of UV light. Inparticular, one of the layers of the diffuser plate, such as thesubstrate 202, may include a UV absorbing material, or the diffuserplate may include a separate layer of UV absorbing material. Suitable UVabsorbing compounds are available commercially, including, e.g.,Cyasorb™ UV-1164, available from Cytec Technology Corporation ofWilmington, Del., and Tinuvin™ 1577, available from Ciba SpecialtyChemicals of Tarrytown, N.Y. The diffuser plate may also includebrightness enhancing phosphors that convert UV light into visible light.

Other materials may be included in one or more of the layers of thediffuser plate to reduce the adverse effects of UV light. One example ofsuch a material is a hindered amine light stabilizing composition(HALS). Generally, the most useful HALS are those derived from atetramethyl piperidine, and those that can be considered polymerictertiary amines. Suitable HALS compositions are available commercially,for example, under the “Tinuvin” tradename from Ciba Specialty ChemicalsCorporation of Tarrytown, N.Y. One such useful HALS composition isTinuvin 622. UV absorbing materials and HALS are further described inco-owned U.S. Pat. No. 6,613,619, incorporated herein by reference.

In other exemplary embodiments, the diffuser plate 300 may bedouble-sided, having a first diffuser layer 304 a on one side of thesubstrate 302 and a second diffuser layer 304 b on another side, as isschematically illustrated in FIG. 3A. The diffuser layers 304 a and 304b may each be applied directly to the respective surface of thesubstrate 302, as is illustrated in FIG. 3A, or may be attached using alayer of adhesive 306 a, 306 b, as is schematically illustrated in FIG.3B.

The double-sided diffuser plate 300 may be symmetrical, with the twodiffuser layers 304 a, 304 b having the same diffusion properties, ormay be asymmetric, with the diffuser layers 304 a, 304 b havingdifferent diffusing properties. For example, the diffuser layer 304 amay possess a different transmission or haze level from the seconddiffuser layer 304 b, or may be of a different thickness.

In other exemplary embodiments, the diffuser plate may include more thanone substrate. One such embodiment is schematically illustrated in FIG.3C, which shows a diffuser plate 320 formed with first and secondsubstrates 302 a and 302 b. Other optical layers in the diffuser plate320 may be positioned symmetrically, with other optical layerspositioned between the substrates 302 a, 302 b, or asymmetrically, withone or more of the other optical layers positioned to the other side ofone of the substrates 302 a, 302 b. In the exemplary embodimentillustrated in FIG. 3C, a diffuser layer 306, is located between thesubstrates 302 a, 302 b, and may be attached to the two substrates 302a, 302 b via adhesive layers 306 a, 306 b. In another approach, wherethe diffuser layer 304 is an adhesive layer, the adhesive layers 306 a,306 b may be omitted.

Another exemplary embodiment of diffuser plate 340 is schematicallyillustrated in FIG. 3D. This diffuser plate 340 includes two substrates302 a, 302 b, with a diffuser layer 304 and a reflective polarizer 308between the substrates 302 a, 302 b. In this particular embodiment, thediffuser layer 304 is also an adhesive layer, and so the diffuser layer304 may be used to attached the reflective polarizer 308 to the lowersubstrate 302 a. Another adhesive layer 306 may be positioned betweenthe reflective polarizer 308 and the upper substrate 302 b.

Other configurations of diffuser plate having two substrates may also beused. For example, additional optical layers, such as a brightnessenhancing layer, may be placed between the substrates, In addition, oneof the substrates may comprise a plate of another element of thedisplay. For example, the upper substrate of the diffuser layer maycomprise the lower plate of the liquid crystal display panel, or thelower substrate may comprise the plate of a flat fluorescent display.Both of these configurations are described further below.

Other exemplary embodiments of a diffuser plate may also incorporateadditional light management layers. For example, a diffuser plate 400may include a substrate attached to one side of a diffuser layer 404,with a reflective polarizer 406 attached to the other side of thediffuser layer 404, as is schematically illustrated in FIG. 4A. Thereflective polarizer 406 may be attached using an optional layer ofadhesive 408, as shown in the illustrated embodiment. Optionally anadditional coating 409 may be provided over the reflective polarizer406. For example, the coating 409 may be a protective hard-coat layer.

In another exemplary embodiment, not illustrated, the diffusing layer404 and the reflective polarizer 406 may be co-extruded as a combinedlayer, without the need for a layer of adhesive 408 between the diffuser404 and the reflective polarizer 406. The combined layer of the diffuser404 and reflective polarizer 406 may then be mounted to the substrate402, for example with an adhesive layer.

In another exemplary embodiment, the diffuser layer 404 is an adhesivelayer, and may be used to mount the reflective polarizer 406 to thesubstrate 402, as is illustrated in FIG. 4B.

In other embodiments, the diffuser layer 404 may itself comprise adiffuse adhesive layer, in which case the reflective polarizer 406 maybe attached directly to the diffuser layer 404. Adhesive diffusivelayers are discussed in greater detail in International (PCT) PatentPublications WO99/56158 and WO97/01610, incorporated herein byreference. Adhesive diffusive layers may be used in any of the diffuserplate embodiments discussed herein.

In addition, a brightness enhancing layer 412, such as a prismaticbrightness enhancing layer, may optionally be used with the diffuserplate 400. The brightness enhancing layer 410 may be attached to thereflective polarizer 406, as is schematically illustrated in FIG. 4C,for example using via an adhesive layer 412. In other exemplaryembodiments, the brightness enhancing layer 410 may not be attached tothe reflective polarizer 406, but may be free-standing relative to thediffuser plate 400, with an air gap between the reflective polarizer 406and the brightness enhancing layer 410.

In another exemplary embodiment 430, schematically illustrated in FIG.4D, a brightness enhancing layer 432 may be attached to the diffuserlayer 404. The brightness enhancing layer 432 may be attached directlyto the diffuser layer 404, for example if the diffuser layer 404 isadhesive, or may be attached to the diffuser layer 404 using anintermediate layer of adhesive 434.

In some exemplary embodiments, it may be desirable for at least some ofthe light to enter the brightness enhancing layer 432 through an airinterface or an interface having an increased refractive indexdifference. Therefore, a layer of low index material, for example afluorinated polymer, may be placed between the brightness enhancinglayer and the next layer below the brightness enhancing layer.

In other exemplary embodiments, an air gap may be provided between thebrightness enhancing layer 432 and the layer below the brightnessenhancing layer. One approach to providing the air gap is to include astructure on one or both of the opposing faces of the brightnessenhancing layer 432 and the layer below the brightness enhancing layer.In the illustrated embodiment, the lower surface 440 of the brightnessenhancing layer 432 is structured with protrusions 442 that contact theadhesive 434. Voids 444 are thus formed between the protrusions 442,with the result that light entering into the brightness enhancing layer432 at a position between the protrusions 442 does so through an airinterface.

Other approaches to forming voids, and thus providing an air interfaceto light entering the brightness enhancing layer, may be used. Forexample, the brightness enhancing layer 432 may have a flat lowersurface 440, with the adhesive 434 being structured with protrusions.These, and additional approaches, are discussed in co-owned U.S. PatentPublication No. 2003/0223216 A1, incorporated herein by reference. Anyof the embodiments of diffuser plate discussed herein may be adapted toprovide an air interface for light entering the brightness enhancinglayer.

Optionally, a reflective polarizer layer 436 may be attached to thestructured surface of the brightness enhancing layer 432. Attachment ofoptical films to the structured surface of a brightness enhancing layeris further described in co-owned U.S. patent application Ser. No.10/439,450, incorporated herein by reference.

Another exemplary embodiment of a diffuser plate 450 is schematicallyillustrated in FIG. 4E. In this embodiment, an air gap 452 is formedbetween the brightness enhancing layer 410 and the layer from which thelight passes to the brightness enhancing layer 410, in this case thediffusing layer 404. The air gap 452 may be formed by providing a layerof adhesive 454 between diffusing layer 404 and the brightness enhancinglayer 410, around the edge of the plate 450. A reflecting polarizer 406may optionally be provided above the brightness enhancing layer 410, andmay be attached to the brightness enhancing layer 410. In a variation ofthis embodiment, brightness enhancing layer 410 may be replaced with areflective polarizer that has a brightness enhancing structure on itsupper side.

Another exemplary embodiment of a diffuser plate 460 is schematicallyillustrated in FIG. 4F. In this embodiment, an air gap 462 is formedbetween the brightness enhancing layer 410 and the diffuser layer 404.The diffuser layer 404 is provided as an adhesive that may be higher atthe edges of the diffuser plate 460 than in the central region. The edgeportions 464 of the adhesive attach to the brightness enhancing layer410. An intermediate layer 466 may be provided in the gap 462, forexample a blank buffer layer or a reflecting polarizer. In thisparticular embodiment, the edge portions 464 of the adhesive are higherthan the intermediate layer 466.

It is generally preferred, although it is not a limitation, that opticallayers placed between the reflective polarizer and the LCD panel, inthis and other embodiments, be polarization preserving. This avoids orreduces adverse affects on the polarization of the light that has beenpolarized by the reflective polarizer. Hence, it would be preferred inthis embodiment for the brightness enhancing layer 410 to demonstratelittle or no birefringence.

In another exemplary embodiment of diffuser plate 470, schematicallyillustrated in FIG. 4G, the edge portions 464 are not higher than theintermediate layer 466. Thus, when the brightness enhancing layer 410 isattached to the edge portions 464, the higher intermediate layer 466bows the brightness enhancing layer 410 out, to produce an air gap 472between the intermediate layer 466 and the brightness enhancing layer410.

In some exemplary embodiments, the lower plate of the LCD panel itselfmay be used as the substrate that supports the diffuser layer and otheroptical layers. One exemplary embodiment of such a display isschematically illustrated in FIG. 5, in which an LCD panel 102 includesan LC layer 104 and upper and lower plates 106 a, 106 b. The plates 106a, 106 b are typically made of glass, or a thick polymer, and may alsoinclude absorbing polarizers. A light management unit 502 is attached tothe lower plate 106 b. The light management unit 502 includes a diffuserlayer 504 and may also include other optical layers. For example, thelight management unit 502 may also include a brightness enhancing layer506 and a reflective polarizer 508. If a brightness enhancing layer is506 is included, then an air gap 510 may be formed at its lower surfaceusing any of the approaches described above. For example, a layer ofadhesive 512 around the edge of the light management unit 502 may beused to provide the air gap 510. The light management unit 502 may beattached to the lower plate 106 b using another adhesive layer 514.

Other layers may also be present in the light management unit 502attached to the LCD panel 102. For example, an additional substrate maybe placed within the light management unit 502.

Some fluorescent light sources, referred to herein as a flat fluorescentlamp (FFL), provide a two dimensional plane or surface that may be usedfor attaching the diffuser layer and other optical layers. These typesof light sources are also known by other names, such as flat dischargefluorescent lamp, and two-dimensionally integrated fluorescent lamp(TIFL). Some FFLs are based on a fluorescently converting the UV outputfrom a mercury discharge, while other FFLs use the discharge of someother material. For example, the Planon II lamp, available from OsramGmbH, Munich, Germany, is a two dimensional fluorescent lamp based on axenon excimer discharge.

One exemplary embodiment of a light management unit 604, comprising adiffuser layer 606 and, optionally, other optical layers, integrated onan FFL 602 is schematically illustrated in FIG. 6A. In this embodimentof integrated light source 600, the FFL 602 has a substantially flatupper surface 603. The light management unit 604 may optionally includeother layers, for example, a reflective polarizer 608 and/or abrightness enhancing layer 610, one or more of which are attached to thediffuser layer 606. In the illustrated exemplary embodiment, thereflective polarizer 608 is attached to the diffuser layer 606. Thediffuser layer 606 may be an adhesive layer, or an additional adhesivelayer (not shown) may be used to attach the reflective polarizer 608 tothe diffuser layer 606.

The brightness enhancing layer 610 may be free standing or may beattached to one or two of the other layers in the light management unit604 using any of the approaches described above. For example, in theexemplary embodiment of integrated light source 620 schematicallyillustrated in FIG. 6B, the brightness enhancing layer 622 is positionedbetween the reflective polarizer 608 and the diffuser layer 606, and hasa lower surface 624 adapted to provide air gaps 626 diffuser layer 606and the brightness enhancing layer 622.

The FFL need not have a flat upper surface. For example, in theembodiment of integrated light source 640 schematically illustrated inFIG. 6C, the light management unit 644 is attached to an FFL 642 thathas a ribbed upper surface 646. The diffuser layer 606 may be attachedto the ribs of such a surface 646.

EXAMPLES

A number of sample diffuser plates manufactured according to thisdisclosure were prepared and their performance was compared to that ofdiffuser plates used in commercially available LCD-TVs. The diffuserplates were tested for single pass light transmission and reflection andfor brightness and uniformity.

Light transmission and reflection measurements of the diffuser platesand substrate materials, for samples S1-S27 and control samples C-1 andC2, were made using a BYK Gardner Haze-Gard Plus instrument, catalog no.4723 and supplied by BYK Gardner, Silver Spring, Md. The transmissionand haze levels were collected according to ASTM-D1003-00, titled“Standard Test Method for Haze and Luminous Transmittance forTransparent Plastics”. The instrument was referenced against air duringthe measurements. In all the measurements for transmission and haze, theD1 side of the diffuser plate was positioned on the same side as theclarity port and the D2 side of the diffuser plate faced the haze port.

The measurements of brightness and uniformity, for samples S1-S27 andcontrol samples C1 and C2, were performed on a specially designed LCD-TVexperimental test bed. The test bed apparatus 700, illustratedschematically in FIG. 7 used two functioning parts: namely i) a 22″Samsung LCD-TV, Model LTN226W, Model Code: LTN226WX/XAA and shown aselement 702 in FIG. 7, and ii) a goniometer stage 704. The goniometer704 allowed the TV 702 to be moved from a horizontal position, used forfilm loading and shown in dashed lines, to a vertical position for themeasurements. This arrangement provided for convenient for convenientloading and testing of various diffuser panels 706. The LCD-TV 702 waslocated about ˜15 feet (about 4.6 m) from a Prometric CCD Camera, Model16111 (shown as element 708 in FIG. 7), obtainable from Radiant Imaging,DuVall, Wash.). The camera was provided with a Radiant Imaging OpticalFilter, 72 mm ND 2.0. The Prometric camera luminance was calibratedusing a Photo Research PR 650 (Chatsworth, Calif., SSN: 60964502). Forthe measurements reported below, the LC panel and absorbing polarizershad been removed from the LCD-TV, and various diffuser panels were usedwith the LCD-TV's backlight. The LCD-TV's backlight included anarrangement of eight parallel CCFL lamps.

The data was averaged across one x coordinate and reported as theluminance in nits, while the standard deviation in the brightness acrossthe diffuser plate was collected on the same data to provide a metric onthe uniformity.

The structural and optical properties of each of the sample diffuserplates and the control samples are summarized in Table I below, andvalues of brightness uniformity are shown plotted against totalbrightness in FIG. 8A. In Table I, each row presents the data for asingle sample. The control samples, C1 and C2, being listed first.

The “Subst.” column lists the type of substrate used. The “Thick” columnshows the thickness of the substrate. The “D1” column lists the type ofdiffuser layer used on the side of the substrate facing away from thelamps. The “D2” column lists the type of diffuser layer used on the sideof the substrate facing the lamps. When the substrate was provided witha single diffuser layer, the optical properties were measured with thediffuser layer facing away from the lamps. The “Luminance” column showsthe total luminance measured for light transmitted through the diffuserplate, in Nits. The “Uniformity” column lists the standard deviation inthe brightness measured across the diffuser plate, also in Nits. Thecolumn labeled “a/x” lists the ratio of the uniformity over theluminance, in other words a relative uniformity. The “Transmit” columnlists the single pass transmission through the diffuser plate. This isthe value of the single pass transmission averaged across the diffuserplate. Where the plate has a uniform diffusion characteristic, thetransmission at any one point is equal to the spatially averagedtransmission. Where the plate has a non-uniform diffusioncharacteristic, i.e. as with a printed pattern diffuser, thetransmission at any one point need not be the same as the spatiallyaveraged transmission. The “Haze” column lists, as a percentage, theratio of the diffuse light transmitted through the diffuser plate overthe total light transmitted through the diffuser plate.

TABLE I Summary of Diffuser Plate Samples and Control Examples LuminanceUniformity σ/x Transmit Haze EXAMPLE Subst. Thick D1 D2 Nits Nits % % %C1 Samsung 2 mm n/a n/a 5422 68 1.3 56.8 103 C2 Sharp 2 mm n/a n/a 5740271 4.7 70.4 103 S1 1737F 1 mm  7725-314 none 5363 3100 57.8 92.3 82.4S2 1737F 1 mm 3635-70 none 5461 286 5.2 62 101 S3 1737F 1 mm 3635-30none 4811 69 1.4 38.2 102 S5 1737F 1 mm  7725-314  7725-314 5638 200835.6 86.8 96 S6 1737F 1 mm  7725-314 3635-70 5399 209 3.9 60.4 102 S71737F 1 mm  7725-314 3635-30 4754 63 1.3 35.8 102 S8 1737F 1 mm 3635-703635-70 5175 86 1.7 50.5 102 S9 1737F 1 mm 3635-70 3635-30 4639 66 1.434.6 102 S10 1737F 1 mm 3635-30 3635-30 4079 44 1.1 24.7 102 S19 PC 2 mm3635-70 none 4996 302 6.0 58.1 101 S20 PC 2 mm 3635-70 3635-70 4740 1012.1 48.1 102 S21 PMMA 2 mm 3635-70 none 5524 249 4.5 60.1 101 S22 PMMA 2mm 3635-70 3635-70 5316 131 2.5 49.9 102 S26 Float 1 mm 3635-70 none5139 120 2.3 56.0 102 S27 Float 1 mm 3635-70 3635-70 4924 110 2.2 43.8102Control Sample C1

Control Sample 1 (C1) is the Samsung Patterned Diffuser Plate thataccompanied the 22″ Samsung LCD-TV (Model: LTN226W). This diffuser platewas a 2 mm thick plate formed of PMMA, and contained CaCO₃ diffusingparticles. In addition, the plate possesses a printed pattern that isregistered to the CCFL bulbs of the Samsung LCD-TV. Control Sample 1 istaken as representing a high performance LCD-TV diffuser plate.

Control Sample C2

Control Sample 2 is the diffuser plate that accompanied a Sharp 30″LCD-TV, model no. LC-30HV2U. This diffuser plate was formed from a 2 mmthick plate of PMMA containing 5 μm glass spheres as the diffusingparticles. This diffuser plate did not possess a printed pattern.Control Sample 2 is taken as representing a standard LCD-TV diffuserplate.

Samples S1-S3: Single Sided Diffusers on LCD Glass

Samples S1-S3 were single-sided diffuser laminates based on a 1 mm thickLCD glass substrate (Corning 1737F) and a variety of diffuser films. Theglass plates were sized to fit into the Samsung 22″ LCD-TV(19.58″×11.18″ with 0.1″×1″ notches in the middle of both horizontaledges). These samples possessed the same sizes as C-1 and C-2. The glassplates of samples S1-S3 were laminated with 3M Scotchcal™ diffusingfilms 7725-314, 3635-70, and 3635-30 respectively, all available from 3MCompany, St. Paul, Minn. The diffuser films provided a diffusioncharacteristic that was uniform across the width of the samples.

The brightness measured across S1-S3 diffuser plates is shown as afunction of position across the plates in FIG. 8B, with the results forcontrol sample C1 shown for comparison. The single pass transmission forthe samples reduces from S1 to S3. As the plate transmission decreasesthe brightness values also decrease. The illumination through the platesbecomes more uniform (reduced a), however, with lower single passtransmission.

Samples S5-S10: Double-Sided Diffusers on LCD Glass

Samples S5, S8 and S10 were prepared the same way as samples S1-S3,except that diffuser films were laminated to both sides of the diffuserplate. Samples S5, S8, S10 were symmetric, in other words the diffuserlayer was the same on both sides of the substrate. The diffuser filmsprovided a diffusion characteristic that was uniform across the width ofthe samples.

Samples S6, S7 and S9 were asymmetric, using different diffusers on thesides of the substrate. Samples S6 and S7 were prepared the same way asS1 except that the second diffuser layer D2, was added, 3635-70 in thecase of S6 and 3635-30 in the case of S7. Sample S9 was prepared thesame way as S9, except that a 3635-30 diffuser layer was added as the D2layer.

The brightness through samples S5, S8 and S10 is shown as a function ofposition across the plate in FIG. 9, along with the measured values forC1. The performance of S8 most closely matches to that of C1: theluminance value for S8 is 5175 nits, compared with 5422 nits for C1, andthe relative uniformity is 1.7% compared with 1.3% for C1, and 4.7% forC2. These data demonstrate that, by proper design of the diffuser platelaminate, a diffuser plate fabricated according to the presentdisclosure can be designed to have optical properties similar to thoseof a patterned diffuser plate.

This set of examples demonstrates that, by proper design of the diffuserelement with the enhancing layers, an optimized light managementassembly can be realized. It is important to realize that the opticalperformance of the laminated samples S2 and S8 approaches that even ofthe high quality diffuser C1. C1 was provided with a patterned diffuser,which increases the cost of the diffuser plate, in order to achieve highuniformity. In contrast, laminated samples S2 and S8 used a uniformdiffuser.

Samples S19, S21 and S26: Single-Sided Diffusers on Different Materials

Samples S19, S21 and S26 were made in the same way as S2, except thatS19 used a substrate of 2 mm thick Lexan polycarbonate (PC), S21 used asubstrate of 2 mm thick PMMA, and S26 used a 1 mm sheet of float glass(Industrial Glass Products, Los Angeles, Calif.). The brightnessmeasurements across the plates are presented in FIG. 10 for S19, S21,and S26, along with the corresponding measurements for S2. Theuniformity levels are similar in all three samples, but the single passtransmission through the PC plate was relatively low. These resultssuggest that the plate material may be an important variable indesigning the diffuser plate.

Samples S20, S22 and S27: Double-Sided Diffusers on PC and PMMA

Samples S20, S22 and S27 were made in the same way as S8, except thatS20 used a substrate of 2 mm thick Lexan PC, S22 used a substrate of 2mm thick PMMA, and S26 used a 1 mm sheet of float glass (IndustrialGlass Products, Los Angeles, Calif.). The brightness measurements acrossthe plates are presented in FIG. 11 for S20, S22 and S27, along with thecorresponding measurements for S8. The uniformity levels are similar inall three samples, but the single pass transmission through the PC platewas relatively low.

Selected Samples with BEF/RP

Samples C-1, C-2, S1-S10 S19-S22, S26 and S27 were modified by placing alayer of Vikuiti™ DBEF-440 reflective polarizer (RP) and a layer ofVikuiti™ BEF-3T prismatic brightness enhancing film (BEF) above thediffuser plate, both films available from 3M Company, St. Paul, Minn.The brightness was measured as a function of position across thedisplay. The results some of these measurements are summarized in TableII, which shows the luminance and the brightness uniformity in terms ofthe standard deviation, σ, in the luminance level across the display,and the relative uniformity, σ/x. For comparison, the relativeuniformity of the diffuser plate when illuminated without the brightnessenhancing film and reflective polarizer is shown in the last column,marked σ/x (D). FIG. 12 shows a graph of uniformity plotted againstilluminance.

The uniformity of the transmitted light improved for all samples, withthe exception of S8, with the addition of the brightness enhancing filmand the reflective polarizer. The uniformity of some of the S-samples,however, improved more than the control samples. For example, theuniformity S2 sample improved from 286 Nits to less than 100 Nits, andthe relative uniformity improved from 5.2% to 1.5%, which was betterthan for C2. The luminance of S2 was approximately the same as for C1.

The illuminance as a function of position across the display is shown inFIG. 13 for samples S2, S8, C1, and C2. These samples possessed on-axisgain values of 1.76, 1.70, 1.78, and 1.90, respectively. C2 showedhigher overall transmission than modified S2, but was less uniform.

TABLE II Summary of Diffuser Performance When Used With BrightnessEnhancing Film and Reflective Polarizer Luminance σ/x Sample (Nits) σ(Nits) σ/x (D) C1 5843.9 58.1   1% 1.3% C2 6076.0 97.9 1.6% 4.7% S25814.2 89.7 1.5% 5.2% S5 5638 73 1.3% 35.6%  S8 5522.2 88.8 1.8% 1.7%S19 4478.1 81.3 1.8% 6.0% S20 4272.8 81.2 1.8% 2.1% S21 5989.0 95.3 1.6%4.5% S22 5726.1 112.8 2.0% 2.5% S26 5298.6 60.0 1.1% 2.3% S27 5052.262.5 1.2% 2.2%

A study of the illuminance uniformity was made for various values oftransmission in the range of about 77%-92%. Various samples like S1 weremade, but with additional layers of the Scotchcal™ ElectroCut™ GraphicFilm, type 7725-314 diffusive layer. The performance of these samples,S1a-S1d is listed in Table III below. Samples S1a-S1d had 2-5 layers ofthe diffuser on each side of the substrate (4-10 layers total),respectively.

TABLE III Uniformity Study For High Transmission Diffusers Sample T % x,nits σ, nits σ/x % C1 56.8 4345 38 0.87 C2 70 4590 49 1.08 S1 92.3 452188 1.94 S5 86.8 4412 46 1.05 S2 62 4351 45 1.04 S1a 85.7 4282 44 1.02S1b 83.1 4104 37 0.91 S1c 80.1 3934 37 0.95 S1d 77.2 3800 35 0.93These results for σ/x also shown in FIG. 19 as a function of single passtransmission, T. The 7725-314 diffusive layer had an absorption ofaround 2%, and so the transmission for samples S1a-S1d was reducedrelative to the transmission of S1. However, the value of σ/x was verygood, in most cases being less than 1%, which shows that a uniformdiffusing layer can provide uniformity values approaching that of apatterned diffuser.

Conventional wisdom holds that increased illumination uniformity isachieved using relatively high levels of diffusion, which meansrelatively lower single pass transmission, typically around 70% orlower. The results presented in FIG. 19 show that the conventionalwisdom is misleading when the diffuser is used in conjunction with abrightness enhancing layer, and that high illumination uniformity can beachieved using a uniform diffuser having a single pass transmissionhigher than 70%. In fact, where the diffuser is uniform, the relativeuniformity is maximum in the range 75%-90%. It is believed that highlevels of uniformity are possible with high diffuse transmission becausethe brightness enhancing layer interacts preferentially with lightdiffused by the diffuser at certain angles. Accordingly, preferredvalues of single pass transmission in the diffuser plate may be greaterthan 75%, 80%, or 85%, and ranges of single pass transmission may lie inthe range 72%-95%, more preferably in the range 75%-90%. These singlepass transmission values correspond to the single pass transmissionthrough the combination of all diffuser layers present in the set oflight management layers disposed between the light source(s) and the LCDpanel.

Further Example Single Sided Acrylic Foam Tape on PMMA

An additional example, Sample S28 was prepared with a 0.4 mm layer ofacrylic foam tape (VHB 4643 tape, available from 3M Company, St. Paul,Minn.) as the diffuser layer on a 3 mm thick PMMA substrate. Thediffusion characteristic of the acrylic foam tape was uniform. Theperformance of this sample, compared with an additional control sample,C3, is shown in Table III. The control sample was the diffuser platetaken from an SEC 40 inch LCD-TV Model No. 400W1 and was based on a 3 mmthick PMMA substrate containing diffusing particles.

TABLE III Performance of Sample S28 compared to that of C3Characteristic C3 S28 Single Pass Transmittance  65%  50% Haze ~100%~100% Diffuser plate only 4509 nit 4431 nit Diffuser Plate + BEF 8229nit 8059 nit Plate + absorbing polarizer 2036 nit 1979 nit Diffuserplate + BEF + abs. polarizer 3542 nit 3440 nit Diffuser plate + BEF +refl. polarizer + abs. 4612 nit 4496 nit polarizer

The single pass transmittance and haze were made as single passmeasurements, while the remaining measurements of illuminance were madewith the diffuser plates in place on the SEC television, using thetelevision's lamps. The illuminance was measured with variousconfigurations of diffuser plate and other light management layers. Thethird row shows the illuminance for the diffuser plate only. In the caseof comparative example C3, the diffuser plate was the PMMA sheet thatcontained diffuser particles. In the case of S28, the diffuser plate wasthe 3 mm thick PMMA plate with an acrylic foam tape diffuser mounted onone side.

The fourth row shows the illuminance when the diffuser plate wascombined with a layer of brightness enhancing film (BEF) (Vikuiti™BEF-3T film produced by 3M Company, St. Paul, Minn.). The fifth rowshows the illuminance when the diffuser plate was combined with theabsorbing polarizer used in the LC panel. The sixth row shows theilluminance when the diffuser plate was combined with the BEF and theabsorbing polarizer. The seventh row shows the illuminance when thediffuser plate was combined with the BEF, a reflecting polarizer(Vikuiti™ DBEF-440 MOF reflecting polarizer), and the absorbingpolarizer.

The single pass transmittance of S28 is a little lower than that for C3,but has a similar level of haze. Also, the illumination performance ofS28 is only a few percent lower than that for C3, which is significantbecause the transmittance of S28 was not optimized for this test.Conoscopic plots showing the output from S28 and C3 are shown in FIGS.14A and 14B respectively. The acrylic foam tape diffuser plate has anearly isotropic distribution, similar to that of C3. Thus, it isbelieved that, with further optimization, acceptable opticalcharacteristics can be achieved in a diffuser plate possible usingacrylic foam tape as a diffuser.

The diffuser plates of the present invention may be fabricated usingdifferent approaches. One particular approach is now discussed withreference to FIGS. 15A and 15B. In this approach, a number of flexiblefilms, for example diffuser, reflective polarizer and/or brightnessenhancing films are first laminated together. The films may be directlylaminated together or may be laminated using one or more intermediateadhesive layers. In the illustrated embodiment, a first film 1502 and asecond film 1504 are taken off respective rolls 1506 and 1508 andlaminated in a lamination roll 1510, as schematically shown in FIG. 15A.The laminated web 1512 may then be wound on a rewinding roll 1514. Thelaminated web 1512 may be a laminate of more than two films.

The laminated web 1512 may then be wound off the rewinding roll 1514, asis schematically shown in FIG. 15B, and laminated onto a series ofsubstrate panels 1516 via a second lamination roll 1518. A cutting edge1520 may be used to kiss cut the laminated web 1512 as it comes off therewinding roll 1514 so as to form a length of laminated web 1512appropriate for lamination to the substrate panel 1516. The cutting edge1520 may instead be used to make a complete cut through the laminatedsheet.

Another approach to fabricating a diffuser plate is now discussed withreference to FIGS. 16A and 16B. In this approach, a number of flexiblefilms, for example, a diffuser film, a reflective polarizer layer and/ora brightness enhancing film are first laminated together. The films maybe directly laminated together or may be laminated using one or moreintermediate adhesive layers. In the illustrated embodiment, a firstfilm 1552 and a second film 1554 are taken off respective rolls 1556 and1558 and laminated in a lamination roll 1560, as is schematicallyillustrated in FIG. 16A. The resulting laminated web 1562 is then cut bya cutting tool 1564 into prepared laminate sheets 1566 of a desiredlength. The prepared laminate sheets 1566 may be formed into a stack1568.

Individual laminate sheets 1566 from the stack 1568 may then be fed by aconveyor system onto respective substrate panels 1570. The conveyorsystem ensures that the laminate sheets 1566 are correctly aligned totheir respective panels 1570. The laminate sheets 1566 may then belaminated to the substrate panel 1570, for example using a laminate roll1572.

Another approach to fabricating a diffuser plate according to thepresent invention is now described with reference to FIG. 17. Substratepanels 1702 are fed to a lamination stage 1704 where they are laminatedwith a number of films. In the illustrated embodiment, the substratepanels 1702 are laminated with two films 1706, 1708 that may be removedfrom respective rolls 1706 a, 1708 b. The substrate panels 1702 mayoptionally have a premask removed before lamination, for example byremoving the premask using a removal roll 1710. Likewise, at least oneof the films 1706, 1708 may have a premask removed, for example bypremask removal roller 1712.

There may be one or more films laminated to the panels 1702 at the sametime. The films laminated to the panels 1702 may include a diffuserlayer, a reflecting polarizer and/or a brightness enhancing layer. Forexample, the intermediate layer 1708 may be a diffuser layer, such as anacrylic foam tape, while the upper layer 1706 is a reflective polarizeror a brightness enhancing layer, or a pre-formed combination ofreflective polarizer and brightness enhancing layer.

After passing through the lamination stage, the laminated panels proceedto a conversion step 1714, for example, where film edges are trimmed andalignment notches are cut into the edges. After the conversion step, thepanels proceed to a handling stage 1716 where they may be, for example,stacked and made ready for shipping.

Another approach to making a diffuser plate according to the presentinvention is now discussed with reference to FIGS. 18A and 18A. In thisapproach, a number of flexible films, for example a diffuser, reflectivepolarizer and/or brightness enhancing films are first laminatedtogether, prior to lamination to the substrate. The films may bedirectly laminated together or may be laminated using one or moreintermediate adhesive layers. This approach may be used to make, forexample, the embodiments of diffuser plate illustrated in FIGS. 4F and4G.

In the approach illustrated in FIG. 18A, a first film 1802, for examplea diffuser sheet, and a second film 1804, for example a brightnessenhancing film, are taken off respective rolls 1806 and 1808 and anintermediate layer 1810 is placed as a sheet between the two films 1802and 1804. The three layers 1802, 1804 and 1810 are laminated together inthe lamination roll 1812 to form a laminated web 1814. The laminated web1814 is then cut into sheets by a cutting edge 1816 to form a stack oflaminated sheets 1818. The laminated sheets 1818 may then be applied torespective substrates, for example in a process similar to that shown inFIG. 16B.

In a variation of the process shown in FIG. 18A, the laminated web 1814is rewound onto a roll 1820 instead of being cut into separate sheets.The rolled, laminated web 1814 may then be applied to substrates, forexample using a method similar to that illustrated in FIG. 15B.

The present invention should not be considered limited to the particularexamples described above, but rather should be understood to cover allaspects of the invention as fairly set out in the attached claims.Various modifications, equivalent processes, as well as numerousstructures to which the present invention may be applicable will bereadily apparent to those of skill in the art to which the presentinvention is directed upon review of the present specification. Forexample, free standing optical films may also be used within an LCDdevice alongside the diffuser plate attached with other optical layers.The claims are intended to cover such modifications and devices.

We claim:
 1. A directly illuminated liquid crystal display (LCD) unit,comprising: a light source; an LCD panel comprising an upper plate, alower plate and a liquid crystal layer disposed between the upper andlower plates, the lower plate facing the light source, the lower platecomprising an absorbing polarizer; and an arrangement of lightmanagement films disposed between the light source and the LCD panel sothat the light source illuminates the LCD panel through the arrangementof light management films, the arrangement of light management filmscomprising at least a first diffuser layer, at least the first diffuserlayer being attached to a lower surface of the lower plate of the LCDpanel, wherein a value of σ/x is less than 1.5%, where x is the level ofillumination light passing from the arrangement of light managementfilms to the LCD panel, averaged across the LCD panel, and σ is the rootmean square deviation in the level of illumination light across thearrangement of light management films.
 2. A unit as recited in claim 1,wherein the single pass transmission through the first diffuser layerand any other diffuser in the arrangement of light management films isin the range of about 72%-95%.
 3. A unit as recited in claim 1, whereinthe value of σ/x is less than 1.3%, and the diffuser plate has a singlepass transmission of at least 75%.
 4. A unit as recited in claim 1,wherein the arrangement of light management films further comprises areflective polarizer and a brightness enhancing layer attached to thelower plate of the LCD panel, the reflective polarizer being disposedbetween the brightness enhancing layer and the lower panel.
 5. A unit asrecited in claim 1, wherein the arrangement of light management filmsfurther comprises a reflective polarizer and a brightness enhancinglayer attached to the lower plate of the LCD panel, the brightnessenhancing layer being disposed between the reflective polarizer and thelower panel.
 6. A unit as recited in claim 1, wherein the arrangement oflight management films further comprises a reflective polarizer attachedto the lower plate.
 7. A unit as recited in claim 1, wherein thearrangement of light management films comprises a stack of least abrightness enhancing layer and a reflective polarizer attached together,the stack being attached to the lower plate of the LCD panel.
 8. A unitas recited in claim 1, wherein the arrangement of light management filmsprovides a spatially uniform diffusion characteristic.